The present invention relates to a machining method using a multiwire saw having a plurality of parallel wires. More specifically, the invention relates to a machining method using a multiwire saw, by which when only one of front and rear surfaces of a wafer or the like is required to be good at machining accuracy, continuous machining process is achieved with high efficiency while maintaining the machining accuracy of the one surface.
Conventionally, the multiwire saw has advantages that the cutting process is achieved with less cutting margins as compared with ID saws (Inside Diameter saws) and that the multiwire saw is superior to the ID saws in machining ability because of capability of carrying out a plurality of cuttings at the same time.
On the other hand, the multiwire saw has a defect of poorer machining accuracy as compared with the ID saws. In particular, because cutting process with the multiwire saw is performed with less cutting margins, the distance between cut objects and the wires is so narrow that the wires may come into contact with cut surfaces of the cut objects during the withdrawal of the wires from the cut objects. This contact may cause the cut surfaces to be flawed, which accounts for a defect of the multiwire saw.
In particular, in the case of a narrow distance between the wires, as shown in FIG. 4A, cut objects 11 at cutting start ends 11a may contact each other due to deformation of cut objects after cutting a workpiece on a mount 13. In such a case, even if a cleaning solution 15 is sprayed from above the cutting start ends 11a, abrasive grains 14 remain between the cut objects 11 without being cleaned away. This accounts for a disadvantage that the cut surfaces of the cut objects 11 may be flawed by the wires 12 or by the abrasive grains 14 remaining between the cut objects 11 when wires 12 are withdrawn from cut objects 11.
In the prior art, therefore, it has been practiced to take a method that the wires are cut upon completion of cutting of the workpiece in order to prevent the cut surface from being flawed when the multiwire saw is separated from the cut objects.
However, with this method in which the wires are pulled out from the cut object by cutting the wires of the multiwire saw, the wires need to be replaced with new ones each time the workpiece has been cut, which may cause cost of wires to be increased and cause operating cycle time of the multiwire saw to be prolonged.
Further, because the wires abruptly lose the tension at the time of cutting the wires, ends of the wires may pop into contact with the cut surfaces of the cut objects in pulling our the wires even with careful work, which may cause the cut surfaces to be flawed.
An object of the present invention is to provide a machining method using a multiwire saw which does not cause any damage to major cut surfaces of cut objects and which can be used a plurality of times without cutting wires of a multiwire saw.
In order to achieve the above object, according to the present invention, there is provided a machining method using a multiwire saw for obtaining a plurality of cut objects by cutting a fixed workpiece with a multiwire saw having a plurality of parallel wires, comprising: a step of cutting the workpiece with the parallel wires of the multiwire saw under a sprinkle of abrasive solution including abrasive grains, thereby obtaining the cut objects; a step of relatively displacing the wires toward one side of cut surfaces of the cut objects; and a step of separating the multiwire saw from the cut objects as the wires remains displaced toward the one side of the cut surfaces of the cut objects.
With this constitution, the fixed workpiece is cut with the multiwire saw having the plurality of parallel wires, by which a plurality of cut objects are obtained. Thereafter, the plurality of wires are displaced toward one side of cut surfaces of the cut objects, or the workpiece is displaced, and then the multiwire saw is separated from the plurality of cut objects. Since the multiwire saw is pulled out after displacing the plurality of wires or after displacing the workpiece toward one side of cut surfaces of the cut objects, the multiwire saw is separated from the plurality of cut objects without causing the wires to contact the cut surfaces opposing the one side of cut surfaces of the cut objects. Therefore, even if the one side cut surfaces of the cut objects are damaged, the other side cut surfaces are not damaged. Further, the wires of the multiwire saw are not cut each time the workpiece has been cut, as has been involved in the prior art, so that the operating cycle time is shortened and the cost is reduced.
In an embodiment of the present invention, a quantity L by which the wires of the multiwire saw are displaced toward the one side of the cut surfaces of the cut objects meets the following condition: Lxe2x89xa7(wxe2x88x92d)/2 where w is a cutting margin and d is a wire diameter.
With this constitution, the wires of the multiwire saw never damage the cut surfaces opposing the one side of the cut surfaces by contacting the one side cut surfaces of the cut objects. Also the wires are separated from the cut objects without causing plastic deformation of the cut objects.
In an embodiment of the present invention, the abrasive grains have a grain size of #2000 or more according to JIS-R6001 so that cutting process damage on the workpiece is reduced.
With this constitution, since abrasive grains having a small grain size of #2000 or more, damage remaining in the cut workpiece is reduced, and the cutting margin is also reduced.
In an embodiment of the present invention, the abrasive grains have a grain size of #3000 to #6000 according to JIS-R6001.
With this constitution, since the abrasive grains have a grain size of #3000 to #6000, damage remaining in the cut workpiece is reduced, and the cutting margin is also reduced. Moreover, the workpiece is cut without lowering the machining efficiency.